1. Field of the Invention
Heretofore, it has been well known to provide studs for tires and particularly studs that are insertable into preformed openings of a tire tread. Such studs have been used to improve the traction of the tier tread with slippery roadway surfaces. The tread of such tires has embedded therein numerous such studs which project from the tire surface by 1.5 to 2.0 mm. The studs are ordinarily provided with hard metal tips to protect them from wearing down. When a vehicle fitted with such studded tires travels over a road surface that is not covered with ice or snow, the road surface is gouged by the hard metal tips of the studs ,and the gouged out material enters the surrounding air in the form of dust. Many states allow studded tire use on roadways during the winter months and prohibit their use during the non-winter months to reduce the road damage and dust problems. This regulation of studded tire use, studded tires allowed half the year and prohibited the other half, causes those members of the public desiring the added traction of studded tires in the winter months to keep two sets of tires, one set studded for the winter and one set non-studded for mon-winter. The purchase of two sets of tires is expensive and causes storage problems.
2. Description of the Prior Art
There have recently been proposed devices which project and retract studs depending on the road surface condition. See U.S. Pat. No. 4,883,104. The studs of these devices are, however, extremely complex in structure, and since they require a source of power (for example, a pneumatic or electrical actuator) for projecting and retracting the studs, they tend to be large in size and high in cost. This has prevented their practical application. Further, some non-skid devices that do not utilize studs have been proposed that show promise in providing protection against slippery roadways without gouging the roadway and raising dust. See U.S. Pat. No. 4,838,329. However, whether these new non-skid devices will provide the needed protection against slippage as well as be commercially viable remains to be seen.
Therefore, there is a need for a tire stud system that is low in cost and reliable in operation, that is capable of preventing slippage on wet or icy roadways and that can be retracted allowing non-studded tire travel on the same tire used during the winter months.